Recent advances in the superconducting transition temperature of various oxide materials has provided the opportunity for applications in radio frequency, microwave and other electronic technologies. Considerable progress has been made in a number of fabrication technologies related to forming these oxide superconductors into various electronic devices. The higher the transition temperature of the superconducting oxide the more likely that material will be of value in such applications. Subramanian, U.S. Pat. No. 4,894,361, and Subramanian et al., Science 242, 249 (1988) disclose superconducting compositions of Tl-Pb-Sr-Ca-Cu-O. Two superconducting phases were identified. One phase has a c-axis unit cell dimension of about 12 Angstroms (1.2 nm) and a superconductivity transition temperature T.sub.c of about 85.degree. K., and the other phase has a c-axis unit cell of about 15 Angstroms (1.5 nm) and a T.sub.c of about 122.degree. K. Methods for producing powders of these materials and single crystals of the higher T.sub.c material are also disclosed.
For most present electronic device applications such as radio frequency and microwave technology, thin films are proving to be the form of superconducting oxide most useful. As a result, much of the work relating to the use of high temperature superconductors in microelectronic applications has focused on the growth of high quality thin films. Such films can serve as ground planes or can be patterned into a microwave circuit. High quality superconducting films can have significantly lower values of surface resistance than copper or gold films. This low surface resistance is important for making high-performance thin film microwave circuits such as filters, resonators and delay lines.
Although the methods of the prior art have achieved quality films, the need exists for further, high quality films. The process of this invention provides high quality superconducting films that include superconducting compositions of Tl-Pb-Sr-Ca-Cu-O. These films are useful as circuit elements.